In Zeep.hs: module Zeep where instance Eq [(Int, Int)] In tst.hs: import Zeep import IOExts The result: bash-2.05a$ hugs __ __ __ __ ____ ___ _________________________________________ || || || || || || ||__ Hugs 98: Based on the Haskell 98 standard ||___|| ||__|| ||__|| __|| Copyright (c) 1994-2001 ||---|| ___|| World Wide Web: http://haskell.org/hugs || || Report bugs to: hugs-bugs@haskell.org || || Version: December 2001 _________________________________________ Hugs mode: Restart with command line option +98 for Haskell 98 mode Reading file "c:\hugs98/lib\Prelude.hs": Type :? for help Prelude> :l Tst.hs Reading file "Tst.hs": Reading file "Zeep.hs": Reading file "c:\hugs98/lib/exts\IOExts.hs": Reading file "c:\hugs98/lib\IO.hs": Reading file "c:\hugs98/lib\Ix.hs": Reading file "c:\hugs98/lib\IO.hs": Reading file "c:\hugs98/lib\Array.hs": Reading file "c:\hugs98/lib\List.hs": Reading file "c:\hugs98/lib\Maybe.hs": Reading file "c:\hugs98/lib\List.hs": Reading file "c:\hugs98/lib\Array.hs": ERROR "c:\hugs98/lib\Array.hs":60 - Cannot justify constraints in instance member binding *** Expression : (==) *** Type : Eq (Array a b) => Array a b -> Array a b -> Bool *** Given context : Eq (Array a b) *** Constraints : Eq [(a,b)] My hugs settings are: +fe.qouiR -stgGlQwkIH -h5000000 -p"%s> " -r$$ -c40 - Conal